1. Field of Inventions
The present inventions relate generally to electrophysiology systems.
2. Description of the Related Art
There are many instances where therapeutic elements must be inserted into the body. One instance involves the formation of therapeutic lesions to the treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia. Therapeutic lesions may also be used to treat conditions in other regions of the body including, but not limited to, the prostate, liver, brain, gall bladder, uterus and other solid organs. Typically, the lesions are formed by ablating tissue with one or more electrodes. Electromagnetic radio frequency (“RF”) energy applied by the electrode heats, and eventually kills (i.e. “ablates”), the tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue. Depending on the procedure, a variety of different electrophysiology probes may be used to position a plurality of electrodes at the target location.
Catheters, which are one type of electrophysiology probe used to create lesions, typically include a relatively long and relatively flexible body that has one or more electrodes on its distal portion. The portion of the catheter body that is inserted into the patient is typically from 23 to 55 inches in length and there may be another 8 to 15 inches, including a handle, outside the patient. The proximal end of the catheter body is connected to the handle which includes steering controls. In the case of cardiac conditions, the length and flexibility of the catheter body allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart, and then manipulated such that the electrodes contact the tissue that is to be ablated. Fluoroscopic imaging is used to provide the physician with a visual indication of the location of the catheter. Exemplary catheters are disclosed in U.S. Pat. Nos. 5,582,609 and 6,287,301.
Surgical probes, which are another type of electrophysiology probe used to create lesions, often include a handle, a relatively short shaft that is from 4 inches to 18 inches in length and either rigid or relatively stiff, and a distal section that is from 1 inch to 10 inches in length and either malleable or somewhat flexible. One or more electrodes are carried by the distal section. In the case of cardiac conditions, surgical probes may be used in epicardial and endocardial procedures, including open heart procedures and minimally invasive procedures where access to the heart is obtained via a thoracotomy, thoracostomy or median sternotomy. Exemplary surgical probes are disclosed in U.S. Pat. No. 6,142,994.
Electrophysiology probes receive power from power supply and control apparatus (also referred to as “electrosurgical units”). The power supply and control apparatus typically monitor tissue temperature through the use of temperature sensors that are carried by the probes. Monitoring tissue temperature and controlling power based on tissue temperature insures that lesions are created (soft tissue coagulation occurs at 50° C.) without over-heating tissue and causing coagulum and charring (over-heating occurs at 100° C.). The electrodes and temperature sensors are connected to the power supply and control apparatus by wires that extend through the interior of the probes. Relatively long electrodes may include a pair of power wires and/or a pair of temperature sensors.
Conventional power supply and control apparatus operate in either a unipolar mode or a bipolar mode. In the unipolar mode, the ablation energy emitted by the electrodes is returned to the power supply and control apparatus through a grounding pad (also referred to as an “indifferent electrode” or a “back plate” or “return electrode”) that is externally attached to the skin of the patient. Power may be controlled on an electrode-by-electrode basis based on the tissue temperatures measured at each of the electrodes. Turning to the bipolar mode, energy that is transmitted to tissue by one or more electrodes is returned to the power supply and control apparatus through one or more return electrodes on the probe. At best, power may be controlled on a “electrode pair-by-electrode pair” basis where one transmitting electrode and one return electrode define a pair. Power is supplied to the transmitting electrode based on the highest temperature measured at the electrodes in the pair.
The inventor herein has determined that, regardless of the type of electrophysiology probe which is used, conventional apparatus and methods for forming therapeutic lesions are susceptible to improvement. For example, the number of electrodes that may be carried by a probe tends to be limited by the number of power and temperature control wires that can be accommodated by the interior of the probe. The inventor herein has also determined that, in the case of unipolar coagulation, the fact that the electrodes have to be relatively close to one another to form continuous lesions, coupled with the aforementioned inherent limitations on the number of electrodes, limits the overall length of the lesions that may be produced by the probes. The inventor herein has further determined that, although the electrodes may be positioned farther apart in the case of bipolar coagulation, the lack of individual electrode control (or “electrode-by-electrode control”) in conventional bipolar systems limits the physician's ability to precisely control lesion length.